Calcium carbonate is well known as a dental abrasive and has long been employed as a primary abrasive in dentifrice compositions such as tooth powders and tooth pastes. It is also well known that fluoride compounds are used commonly to inhibit or reduce dental caries. Fluoride is believed to reduce the solubility of tooth enamel through the interaction of hydroxyapatite, the mineral which constitutes the major part of the dental enamel, with the fluoride so as to produce fluoroapatite which has a lower solubility in the acidic medium.
One of the disadvantages in the use of calcium carbonate dental abrasives is the "chalky" taste characteristic thereof. A second disadvantage in the use of calcium carbonate is that fluoride ion stability in its presence is usually low.
Japanese Patent No. Sho 30812 teaches a coating of calcium pyrophosphate on CaCO.sub.3 using pyrophosphoric acid. While this product eliminates the chalky taste, the fluoride stability of the product is poor.
Japanese Patent No. Sho 30813 describes a process for preparing pyrophosphate-coated CaCO.sub.3 using a salt such as CaCl.sub.2. As would be expected, the presence of a chloride in the process is deleterious to processing equipment. Fluoride stability, while better than that demonstrated in Japanese No. 30812 is less than optimum.
If a way could be found to substantially reduce or eliminate the "chalky" taste of calcium carbonate without adversely affecting fluoride stability, and without using a corrosive salt, as in Japanese No. Sho 30813, such a method would constitute a significant advance in the art and is an object of this invention.